1. Field of the Invention
The present invention relates to a female terminal of the ribbed type and, in particular, to a ribbed terminal having a pin lead-in portion.
2. Description of the Prior Art
U.S. Pat. Nos. 4,545,757 and 4,545,638, both to Neidich and both assigned to the assignee of the present invention, disclose and claim a female connector having terminals of the ribbed type. Such a terminal is used in a connector which is manufactured and sold by E. I. Du Pont de Nemours and Company, Incorporated under the Trademark RIB-CAGE.TM.. This terminal has a central spine from which extends one or more pairs of cantilevered beams. The beams in each pair may be angled forwardly or rearwardly (that is, toward or away the input end of the terminal) and are formed into a structure generally reminiscent of a human rib cage. The ribbed structure defines a generally enclosed opening. The terminal is itself received in a cavity formed in a housing. The housing may have chamfered lead-in portions which serve to guide a pin into the cavity and into the opening defined by the rib cage.
While such a ribbed terminal is an effective connecting mechanism, relatively high insertion forces may be required to insert the pin into the terminal. FIG. 1 graphically illustrates the magnitude of pin insertion force as a function of insertion distance into a connector having a ribbed terminal, wherein the terminal has two bridged pairs of rearwardly extending ribs. The insertion distance is measured with respect to a reference line R that extends perpendicular to the axis of the opening of the terminal and which contains the forward most extremity of the terminal. The location of the reference line R for a connector having a ribbed terminal therein is shown in FIG. 9.
As seen in FIG. 1 there is associated with a terminal as is available in the art a contact lag distance (Distance A, extending from the reference line R to the point d.sub.1 on FIG. 1). The contact lag distance is the distance the pin must be displaced inwardly from the reference line R until a portion of the pin (in the case of the prior art terminal, a portion of the tip of the pin) first encounters the ribs of the terminals. This point marks the location where continued forward displacement of the pin would begin to open the ribs. Because the diametrical (or diagonal) dimension of the major portion of the pin is greater than the dimension of the opening in the rib cage the major portion of the pin remains on the outside of the terminal opening during an initial phase of insertion (Distance B, between the points d.sub.1 to d.sub.2). The insertion force during this phase acts to spread apart the ribs of the terminal, but owing to the relatively poor pressure angle that the tip of the pin occupies with respect to the ribs a relatively high peak insertion force is required before the cage is spread sufficiently to accommodate the pin. Since this force is transmitted to an resisted by the spine of the terminal the column strength of the spine must be of sufficient to withstand this force without buckling. Moreover, if the spine is made thicker or wider it becomes less flexible, thus limiting its ability to move within the housing to accommodate normal misalignments between the pin and the terminal.
Once the peak force is reached the full diameter portion of the pin is abruptly received into the opening of the terminal. Thereafter the level of insertion force required to insert the pin should be relatively constant and is related primarily to the friction force between the pin and the ribs of the terminal (Distance C, between points d.sub.2 to d.sub.3 on the graph of FIG. 1). It should be noted that once the peak insertion force is reached the plot of insertion force versus distance would be expected to drop precipitously, as indicated by the cross portion of the trace in FIG. 1. However, in practice it may occur that the spine may bend and disorient the terminal within the connector housing. Due to this disorientation a higher than expected insertion force may be required in the Distance C, as is indicated by the solid line on the graph of FIG. 1.
During retraction of the pin (Distance D, between points d.sub.3 to d.sub.4 on the graph of FIG. 1) the magnitude of the withdrawal force (acting in a direction opposite the insertion force) should decrease. This is understandable since friction is again the primary force which must be overcome to withdraw the pin and the normal force exerted on the pin by the terminal would decrease as the pin is withdrawn from the terminal. The artifact (Distance E, between points d.sub.4 to d.sub.5 on the graph of FIG. 1) is believed due to the terminal acting to affirmatively expel the pin from the interior thereof as the tip of the pin is reached, analogous to the high peak insertion force required on entry.
The requirement of the relatively high peak insertion force for a given pin, when multiplied over a relatively large number of pins (as those disposed in a multi-pin header) may be difficult to achieve manually. As a result, the use of auxiliary equipment may be required or the number of pins available in a header may be limited. Accordingly, in view of the foregoing it is believed advantageous to provide a terminal of the ribbed type that includes a lead-in portion on the terminal itself to reduce the insertion force required to introduce a pin thereinto.